Table



Feb. 11, 1958 P. A. JENNINGS 24,431

AGE-HARDENING AUSTENITIC STAINLESS STEEL Original Filed Dec. 31, 1952Carbon 0.08% 10 [.50Z Chromium I22 f0 30% Manganese 7% f 2 Nitrogen 0.1% to 0.60%

Silicon pr: no r owr" 0.45)., [ran remainder 1 INVENTOR PAUL 4; JENNINGSATTORNEY United States Patent Ofitice Re. 24,431 Reissuecl Feb. 11, 1958AGE-HARDENIN G AUSTENITIC STAINLESS STEEL Paul A. Jennings, Baltimore,Md., assignor to Armco Steel Corporation, a corporation of Ohio OriginalNo. 2,698,785, dated January 4, 1955, Serial No. 328,882,-December 31',1952. Application for reissue February 20, 1957, Serial No. 641,793

8 Claims. (Cl. 75-126) .Matter enclosedin-heavy brackets appears-in theoriginal patent. but. forms. no part of this reissuespecification;matter printed in italics indicates the'additions made byreissue.

"then" co-pending application- Serial' No. 786,976, filed November 19,1947, now abandoned, which in turn is a continuation-in-part of myapplication, Serial No. 762,863, filed July 23, 1947, also abandoned,and'the invention relates to high temperature stainless steel,especially to articlesin the form of valves, valve parts and otherinternal combustion engine components intended for use while hot incorrosive atmospheres.

Amongthe objects of my'invention is the provision. of strong, tough anddurable stainless steel, and various internal combustion engine valves,and engine components fashioned of the same for elevated temperatureuse, which steel, products function in a highly satisfactory manner insuch fields -as passenger car, truck, aircraft, diesel and marinevesselrengine use, and which offer great'hardnessat the hightemperatures encountered in=such use and substantial resistance,in-theheated condition, to hot corrosive, atmospheres such as thosecontainingthe combustion products; of-anti-knock gasolinesillustratively of the tetraethyl lead :and lead bromide varieties;

Other objects of-myinventionin. part will be obvious andinpart pointedout more fully hereinafter.

The inventionaccordingly consists in the" combination of elements,composition of materials and in the several products; asdescribed'herein, the'scope of: the application of which is, indicated:in the following claims.

The: single figure' of the accompanying drawingrepresents a specific;product. and steel composition thereof falling;within1the scopetofxmyinvention;

As-vconductive' to a clearer understanding of certain features ofmyinvention, it-may be noted at this point that great" variety ofheretofore known valves and valve parts intended for use aszoperatingcomponents of internal combustion engines or thexlike have becomeobsolete for such reasonsas increased engine temperatures'incident togreater engine power and speed; In average passenger cars, for example,the temperatures encountered by the valves frequently areas high as 700degrees F. or -more at-th'efuel intake position, and ashighas1100degrees:-F. to' l'4i0 degrees F. 'or more-at the exhaustposition. These temperatures ordinarily are even higher 1 in truck, bus,marine vessel, or-aircraft engines, especially in' the region Where theexhaust valves operate,

Low-alloy steel valves, for example, which formerly operatedsatisfactorily in internal combustion engines now are found in mostinstances to be unacceptable, and particularly so on the'exhaust side ofthese engines. The valves usually burn or warp very quickly at the highoperating temperatures, thus impairing engine efiiciency and requiringfrequent replacement. While hot, theworking parts commonly develop oxidescale which detrimentally afiects proper seating. In' turn, failure ofthe valve to seat properly allows leakage or blow-by of the hot gases,thus increasing the valve temperature and burning away the metal. An'example of this type valve is one containing about 0.45% carbon, 8.50%chromium, 3.25% silicon, and the remainder substantially all iron.

Also,'mos't of the low-alloy steel valves, including those having thecomposition just noted, are extremely susceptible to active corrosiveattack by leaded fuels and particularly by the hot combustion productsof these 'fue'ls. There are anti-knock fuels containing lead on themarket, which, when consumed, not only exert a ruinous effect uponsteel'valves of low-alloy content, buta great majority of relativelyhigh-alloy steel valves and parts likewise sutfer great detriment andrapid deterioration when exposed to the fuel combustion products.

A number of stainless steel valves, and valves made of other high-alloymetal, for example, have been introduced for better serving present-dayneeds. Some of these are of ferri'tic grade steel. Others arema'rten'sitic. In some, there is a high-silicon content and, as aresult, they enjoy adequate-scaling resistance. Unfortunately, however,theyhave poor resistance tolead compounds and are'decid'edly' inferiorin matters ofhot-ha'rd'ness and stretch resistance under certainoperating conditions.

There are still other valves in the prior art, thesebeing ofaust'eni'ticchromium-nickel stainless steel grade. The amounts ofsilicon inthe conventional austenitic steel products range from about0.50% to 4.0% or more. In general, the austenitic steel valves have amore favorable lattice structure for resisting stress-rupture and creepat elevated temperatures than do the ferritic or martensitic products.It' is also true that the relatively high-alloy content of thechromium-nickel austenitie steel favors resistance to scaling from heatat engine temperatures. A further advantage often arising fromaustenitic steel valve products is their freedom from phasetransformation and, in this respect, freedom from volume changes and anyresulting tendencies such as warping, sticking or cracking during theheating and cooling cycles brought about by the heat engine and itsoperation. The many valves of this character in the prior art, however,leave much to be desired of resistance to corrosive attack by hot leadcompounds.

An outstanding object of my invention, accordingly, is the provision ofa high temperature heat-resistant, corrosion-resistant stainless steeland various valves, valve parts and internal combustion enginecomponents fashioned of the same having substantial strength at thetemperatures of use, which are substantially free of phasetransformation, are hot hard, resist stretch, and efficiently andreliably resist oxidation in the presence of heat and leaded fuelcombustion products.

Referring now more particularly to the practice ofmy invention, 1provide low-silicon, high-nitrogen austenitic chromium-manganesestainless steel internal combustion engine valves, valve parts, andvarious other internal combustion engine components made of thesteel;fillustratively valves, stems,- heads, springs, casings;claddings, linings or surfacings; In preferred composition, my productsinclude about 0.08% to 1.50% carbon, from 12% to 30% chromium, less thanabout 2% nickel, amounts of manganese ranging from to with the siliconcontent not exceeding 0.45%, with nitrogen from 0.06% to 0.60%, and theremainder substantially all iron. Moreover, the sum of the nitrogen andcarbon contents amounts to at least 0.40%. And the relative amounts ofcarbon, chromium, nickel, manganese and nitrogen are such as to yield asubstantially fully austenitic structure.

Preferably, for desired hardness at the high temperatures encountered inactual use, the carbon content amounts to some 0.40% to 1.50% and thenitrogen from 0.20% to 0.55%.

By maintaining a substantial manganese content and the silicon contentbelow about the 0.25% figure, I find sharp improvement in resistance ofthe steel products to corrosion and attack by products by combustionresulting from the burning of leaded fuel. At about 0.15% silicon and ondown to 0.10% or less, this improvement is even more pronounced, and thehot-hardness is not adversely afiected. Both the hot-hardness andcorrosion-resistance are even more favorable where the carbon exceedsabout 0.40% and the silicon ranges from about 0.15 on down substantiallyto zero in amount. The smaller quantities of silicon accordingly areusually preferred.

The inclusion of manganese results from my discovery that nickel insteels of the stainless grade often has an adverse eflect upon thecorrosion resistance of valve products while the latter operate in thepresence of hot lead compounds. By supplanting the nickel ordinarilyrequired for providing a steel of austenitic quality with manganese anaustenitic balance steel is bad and the adverse effect of nickel uponcorrosion resistance in the combustion products of leaded fuels isimportantly dispelled. Moreoven'it seems that the steel of highmanganese content has a greater solubility for carbon and as suchpermits greater hot hardness as higher temperatures are achieved.Additionally it has a much greater solubility for nitrogen.

In my steel I use the element nitrogen in amounts from 0.06% up to about0.30% or 0.40%, or even up to about 0.60%, as a substitute for anequivalent amount of nickel in the steel, in which event the carboncontent may be as low as 0.08%. The nitrogen serves the function ofincreasing the hot-hardness of the steel. And as previously noted italso serves as a partial substitute for other austenite-forming elementsto maintain the austenitic balance.

There are occasions where my stainless steel products include in thealloy composition thereof, as for special purposes, one or more suchelements as molybdenum, titanium, columbium, tungsten, vanadium, copper,cobalt, tantalum, aluminum, zirconium, or the like, ranging from quitesmall amounts to substantial amounts not inconsistent with propertiesdesired.

The stainless steel valves, valve parts and engine components which Iprovide have a sulphur content which may be some quantity below about0.04%, or even as much as 0.2% or more. The larger quantities ofsulphur, and especially those between about 0.15% to 0.20%, contributeto the effect of the low-silicon content in promoting resistance toattack by the combustion products of leaded gasolines and the like. Thelarger quantities of sulphur, say those beyond about 0.04%, andespecially from 0.04% to 0.15%, usually improve the machining propertiesof the steel. Amounts of sulphur much beyond 0.20% often introduce hotworking difficulties with certain of the austenitic steels which Iemploy; also, the rate of improvement of resistance to lead oxidecorrosion usually decreases for these greater amounts. The phosphoruscontent of my products preferably is below about 0.04%.

The particular amounts of such elements as chromium, manganese andnitrogen present in the internal'combustion engine products which Iprovide assure excellent,

4 heat resistance and resistance to oxidation at the high temperaturesencountered. Also, the inclusion of nitrogen and the restriction ofsilicon to the critically small amounts indicated, contribute tocorrosion-resistance of the products, in the combustion products ofleaded fuels, as where the steel takes the form of an exhaust valve orpart exposed to aircraft, truck or passenger car engine exhaust gases.By virtue of the austenitic quality of the steel, my valve productssufier substantially no phase transformation during heating and coolingcycles and, accordingly, are free of volume changes and difficultiesoften following upon change of phase. The valves are strong, tough andhot hard at the high temperatures encountered. They resist scaling,warping and cracking at full temperature and upon being cooled andreheated.

The efiect of the nitrogen addition upon hot-hardness is demonstrated bythe comparative figures given in Table I below. The samples analyzeapproximately 21% chromium, 9% manganese, nickel up to about 2%, 0.10%silicon, .50% carbon, with varying nitrogen contents and remainder iron.All samples were heated at about 2150 degrees F. for one hour, thenwater-quenched, and finally aged at a temperature of about 1350 degreesF. to 1400 degrees F. The hot-hardness tests were made with a cold ballpenetrator at 1400 degrees F. and are reported in Brinell numbers. Thecorrosion tests were made by immersing the samples in molten leadoxy-bromide contained in a new magnesia crucible at a temperature of1550 degrees F. for one hour, the weight loss being reported in gramsper square decimeter.

TABLE I Influence of nitrogen on hot-hardness and resistance to leadoxy-bromide of chromium-manganese stainless steel In Table I it is notedthat with nitrogen in the amount of 0.30% (sample 6374) a hardness ofBrinell is had but with 0.40% (sample 6492) this amounts to 185. Also itis noted that the weight loss in molten lead oxybromide decreases from10.18 grams per square decimeter per hour to 4.59. As a further point itis observed that with an increase in nickel content (sample 6389 ascompared with 6374) there is a slight loss of hothardness (152 Brinellas compared with 155) and a substantial loss in resistance to moltenlead oxy-bromide (17.60 grams per square decimeter per hour weight lossas compared to 10.18)

The eflect of nitrogen as a substitutefor nickel is es peciallyemphasized by hardness tests taken at various high temperatures andillustrated in Table II given below, where two samples of a 21%chromium, 9% manganese stainless steel are presented, one being of lownitrogen and high nickel content, another of low nickel and highnitrogen content. In both cases the samples were annealed at 2150degrees F. for one hour and then waterquenched followed by aging at 1350degrees F. fornine hours and water-quenched. Here as before, thehothardness tests were taken with a cold ball penetrator and reported inBrinell and as to the corrosion tests were made in molten leadoxy-bromide at 1550 degrees F. for one hour and the weight loss reportedin grams 'per square decimeter per hour. Additional corrosion tests weremade at a temperature of 1675 degrees in molten lead oxide contained inmagnesia crucible. the weight loss being similarly reported.

2 TABEE' IIM) Influence 'oriii'trogenon-hobhardness at varioustemperatures, analysis ofsamples From the above it will be seen that theexample having a nitrogen content of 0.40% (sample 6492) issubstantially harder at the respective temperatures of 1400 degrees F.,1500 degrees F. and 1600 degrees F. than the example with the lownitrogen content but with a 4.0% nickel content (sample 49369). Also itwill be seen that there is much less corrosive attack by molten leadoxybromide, although somewhat greater attack by the molten lead oxide.

Certain further benefits are had by the inclusion in my stainless steelof molybdenum in amounts up to about 9%; generally satisfactory resultsare had with molybdenum amounting to about 2% to 5%. The particularbeneficial effects on hot hardness are illustrated by the results givenin Table 1 1-1 below in which, for a 21% chromium, 9% manganesestainless steel with about 0.60% carbon and 0.30% nitrogen, varioushardness figures are given for samples of difiering molybdenum contents.In each case the sample was heated to about 2150 degrees F. for onehour, then water-quenched and finally aged at a temperature of about1350 degrees F. to 1400 degrees F. And, as before the hot-hardness testswere made with a cold ball penetrator at 1400 degrees F. and reported inBrinell numbers. The corrosion tests likewise were made by immersing thesamples in molten lead oxy-bromide contained in a magnesia crucible at atemperature of 1550 degrees F. for one hour and the weight loss reportedin grams per square decimeter per hour.

TABLE III Influence of molybdenum on hot-hardness and resistance to leadoxy-bromide of chromium-manganese-nitrogen stainless steel Hothard- LeadSample 0 Mn Si Cr N1 M0 N ness, oxybro- 1,400 F. mide and other internalcombustion engine components, it will be understood thatcertainadvantages of the invention are bad with other products of thelow-silicon steel, among which are high-temperature gas turbine nozzles,turbine parts adjacent to the nozzle, and any of a variety ofsupercharger components.

While all the benefits of my invention are enjoyedin the steel articlesdescribed above, certain of these benefits, including great hardness athigh temperatures, are enjoyed even where. the silicon content of thesteel is not restricted to the maximum 'figure of 0.45% but is includedin amounts up to 4.0% or even more.

As many possible embodiments may be made of my invention and as manychanges may be made in the em bodiment hereinbe'fore set forth, it willbe understood that all matter described herein is to be interpreted asillustrative and not as a limitation.

I claim as my invention:

1. Age-hardening austenitic stainless steel having a hardness when agedexceeding Brinell at a temperature of 1400 F. and containing about 0.08%to [1.50%] 1.00% carbon, 12% to 30% chromium, 7% to 20% manganese, [.1%]30% to 0.60% nitrogen, silicon up to 4.0%, with the sum of the carbonand nitrogen contents at least 0.40%, and with the various elements allin such proportions as to assure a substantially fully austeniticstructure, and the remainder substantially all iron.

2. Age-hardening austenitic stainless steel having a hardness when agedexceeding 145 Brinell at a temperature of 1400 F., and containing about0.08% to 1% carbon, 19% to 23% chromium, 7% to 11% manganese, molybdenumup to 9%, [.1%] 30% to .60% nitrogen, silicon up to 4.0%, with the sumof the carbon and nitrogen contents at least 0.40%, and the remaindersubstantially all iron.

3. Age-hardening austenitic stainless steel having a hardness exceeding145 Brinell at a temperature of 1400 degrees F. and substantialresistance to corrosion in the presence of leaded fuel combustionproducts, and containing about .08% to .7% carbon, 19% to 23% chromium,7% to 11% manganese, 0.20% to 0.55% nitrogen, incidental amounts ofnickel, silicon not exceeding 0.25%, with the sum of carbon and nitrogencontents at least 0.40%, and the remainder substantially all iron.

4. Age-hardening austenitic stainless steel having a hardness exceeding145 Brinell at a temperature of 1400 degrees F. and substantialresistance to corrosion in the presence of leaded 'fuel combustionproducts, and containing about .08% to .7% carbon, 19% to 23% chromium,7% to 11% manganese, 2% to 5% molybdenum, .1% to .4% nitrogen, siliconnot exceeding 0.25%, with the sum of the carbon and nitrogen contents atleast 0.40%, and the remainder substantially all iron.

5. Age-hardening austenitic stainless steel having a hardness exceeding145 Brinell at a temperature of 1400 degrees F. and substantialresistance to corrosion in the presence of leaded fuel combustionproducts, and containing about .08% to 1% carbon, 19% to 23% chrorium,7% to 11% manganese, nickel less than 2%, sulphur up to 0.15%,molybdenum up to 9%, [.1%] 30% to .60% nitrogen, silicon not exceeding0.45 with the sum of the carbon and nitrogen contents at least 0.40%,and the remainder substantially all iron.

6. Age-hardening austenitic stainless steel internal combustion engineexhaust valves comprising approximately .08% to .7% carbon, 19% to 23%chromium, 7% to 11% manganese, 2% to .55 nitrogen, with the sum of thecarbon and nitrogen contents at least about 0.40%, silicon up to 4.0%,and the remainder substantially all iron.

7. Age-hardening austenitic stainless steel internal combustion engineexhaust valves comprising approximately .08% to .7% carbon, 19% to 23%chromium, 7% to 11% manganese, .1% to .60% nitrogen, molybdenum up to5%, nickel less than 2%, sulphur up to 0.15%, silicon not exceeding0.45%, with the sum of the carbon and nitrogen contents at least about0.40%, and the remainder substantially all iron.

8. Age-hardening aastenitic stainless steel having a hardness exceeding145 Brinell at a temperature of 1400 F., and containing about .08% to.7% carbon, 19% to 23% chromium, 7% to 11% manganese, 20% to 0.55%nitrogen, silicon up to 4.0%, with the sum of the carbon and nitrogencontents at least 0.40%, and the remainder substantially all iron.

References Cited in the file of this patent or the original patentUNITED STATES PATENTS De Vries Aug. 27, 1940 Lorig July 31, 1945Jennings Jan. 31, 1950 FOREIGN PATENTS Switzerland June 1, 1939 OTHERREFERENCES

